In particular, the report said, 10 gusset plates that hold beams in an interlocking pattern are severely eroded.

Of 346 bridge parts inspected, 86 were given a "1" rating, meaning that they were deemed "incapable of perfoming required task."

The 2011 report was dated June 11, and the Transport Ministry banned most traffic from the bridge three days later, citing the need for critical repairs to remedy safety-threatening corrosion and rust.

But Transport Minister Pierre Moreau was quick to point out that long-term repairs to remedy decay were underway when the span was shut down.

"The deterioration was going at a faster rate than what we expected," but the bridge was in no danger of collapsing, Moreau said at a news conference Monday.

Rust was so advanced on some bridge sections that perforations were visible to inspectors. (CBC)

All emergency repairs have been completed, but other work is in progress.

The Mercier Bridge partially reopened Sept. 6, with remaining lanes scheduled to open in December if all repairs are completed.